Arc extinguishing system



Nov. 25, 1952 A. c. VAN DORSTEN ,619,524

ARC EXTINGUISHING SYSTEM Filed April 26, 1946 POWER 1 4 SOURCEJOUJPCZ'OF 8 0,4200% 19 mm o E soma'ar 2 -15 ammo 3 5 .24 mm POWERSOURCE O I 1 1 1 2. K 32 25 VD SEQUENTIALLY 0212,4221: RELAY 15F!c'ozvzAcz's czosz 521m: RIGHT cawmcz's INVENTOR. ADRIANUS COMLLS IZWDOBS'JZN p-d BY (6A5 PRESSURE-HECTRODE I Patented Nov. 25, 1952 ARCEXTINGUISHIN G SYSTEM Adrianus Cornelis van Dorsten, Eindhoven,Netherlands, assignor, by mesne assignments, to

Hartford National Bank and Trust Company,

Hartford, Conn., as trustee Application April 26, 1946, Serial No.665,307 In the Netherlands April 25, 1942 Section 1, Public Law 690,August 8, 1946 Patent expires April 25, 1962 4;- Claims. 1

The invention relates to a device for switching off direct oralternating current, which consists of a mechanical switch which hasconnected in parallel with it a mercury cathode gasor vapourdischargetube which, after the switch has been opened, is automatically ignitedand is then forcedly extinguished.

Although such a device is fundamentally known it has never been foundpossible in practice, more particularly for switching direct current oflarge power of, say, some tens of kilovolts and of some hundreds ofamperes, to realize such a device.

The invention is based on the recognition that this 'is really possibleif a series of exactly determined requirements is satisfied.

According to the invention, the device has the following features:

(a) The tube is ignited within a limited period of time t1 from themoment at which the switch is opened, in such manner that in themeanwhile sparking or arcing to a degree detrim ntal to the contacts isavoided.

(b) The tube is extinguished within a period of time H which is sochosen that within the time ti-l-tz the contacts have been suiiicientlyspaced apart and the space between the contacts has been sufficientlydeionized to prevent renewed sparking or arcing at the contacts due tothe returning voltage.

(c) Re-ignition of the tube due to the returning voltage is avoided, onthe one hand, by the use of a tube of such small dimensions and, on theother hand, by the choice of a thus limited time period t2and hence of alimited increase of pressure due to the tube being heated by the passageof current during the time interval 252- that the product of gaspressure p and electrode spacing d at the end of the period t2 islocated below a determined critical value.

By a determined critical value should he meant hereinafter a value or"the product pd which is located in the region in which the breakdownvoltage increases with the decrease of the value of pd (Paschens curve)and the magnitude of which depends upon the value of the returningvoltage.

It may be pointed out here that at high voltages the desired effectcannot be obtained with a tube of excessively large dimensions so thatin this case in the first instance a tube of the smallest possibledimensions is to be preferred. Since with a decrease of the dimensionsalso the thermal capacity of the tube decreases, this implies that witha smaller tube also the period 162 must again be shorter in order tosatisfy the condition of a suificiently low vapour pressure.

However, this cannot be continued unlimitedly since in the connectionmentioned under (1)) the time period is plays a certain part, foraccording to (b) the total of the time periods t1 and t2 should be sochosen that there exists the possibility of (is-ionizing the spacebetween the contacts to a suificient extent. In this case there existdifferent possibilities with respect to the determination of ti and 152.For a clear apprehension it should, however, be mentioned beforehandthatthe desired high re-ignition voltage may be obtained in any knownmanner, for ex ample byopening the contacts to a sufiicient extent, byutilizing an air current, by providing the contacts in another mediumsuch as oil, etc. and by any combination of these steps.

If now in connection with the production of sparks at the contacts for751 the highest allowable value is taken, only the period of time is isavailable for the de-ionization with the above-mentioned means, whichperiod must therefore have in this case a certain minimum value.Dependently upon the switched voltage and current the time period 152may, however, be reduced still further, to wit by reducing the period trAt a comparatively low voltage and with a high current intensity adecrease of ti affords, comparatively to the case of a high voltage witha high current intensity, less ionization in the are between thecontacts due to this reduction of time. In this case the space betweenthe contacts can be de-ionized more easily and the period 752 can betaken accordingly shorter than the abovementioned minimum value, whichis also desirablein view of the high current intensity taken over by thetube. The returning voltage is comparatively low so that even acomparatively small distance between the contacts may prevent theproduction of a new are after the time t1+t2. In this case it is indeedadvisable already in itself, in connection with the high currentintensity, to take the period t1 not at its maximum.

If, on the other hand, the voltage is comparatively high and the currentintensity is low, t1 may be taken slightly longer than in the precedingcase since due to the high voltage a larger distance between thecontacts is desirable and the low current intensity brings about lessionization, which is, however, increased again due to the longerduration of h. The period t2 may be larger in this case since firstlyalso the current taken over by the tube is of low intensity so thatunadmissible heating and, attended therewith, an unadmissible vapourpressure occur less rapidly and. secondly the ionization brought aboutdue to the longer duration of 21 requires a longer de-ionization period.

It follows from the above that the choice of the lowest and highestallowable values of ti and 132 as well as that of the total of theseperiods is based on a compromise which depends in any particular caseupon the voltage and the current intensity which are to be switched andon the choice of the dimensions of the tube. In general it may be saidthat 252 and ii are of the order of magnitude of seconds.

It should furthermore be mentioned that the practical possibility ofswitching off a high current intensity at a low voltage according to theinvention, which possibility appeared from experiments, alsodemonstrates the possibility of switching off short-circuit powers inelectric high-voltage networks, for in the switching off operation thehigh voltage is not applied to the switch but to the load so that in thefirst instance only the high current intensity has to be taken intoaccount, the switching ofi thereof being now possible in virtue of theabove. In this connection only the high voltage which returns after theswitch has been opened and the parallel tube has been extinguished isimportant, which consequently implies that steps must be taken againstthe renewed production of an arc between the contacts and, as the casemay be, within the tube. Such steps are known, however, so that it maybe expected that they will not give rise to particular drawbacks. I

According to a further feature of the invention, the mechanical switchis constituted in the manner known per se by two or more than twomechanical switches which are located in series and which are to beopened simultaneously and which, for example, may be coupled with oneanother, owing to which, more particularly in switching high currentintensities at a high voltage, the certainty that upon the return of theswitching voltage arcing between the switch contacts is avoided isobtained even in the case of comparatively small distances between thecontacts. In connection with the switching-off rapidity of mechanicalswitches, which rapidity is tied down to determined maximum limits, thisis particularly important in carrying out the invention, when very shorttime periods have to be combined in the correct manner to apredetermined program. Owing to the fact that the total voltage if twoarcs located in series is accordingly higher than the voltage of asingle arc of the same length as that of the two arcs together we obtainthe advantage that the anode voltage of the parallel tube, which voltageis determined by the total of the arc voltage, is higher so that thetube can be ignited more easily at the correct instant. The certainty ofcorrect ignition increases practically to 160% even with the use of twoswitches.

According to one suitable embodiment of the invention the tube isignited with the aid of means controlled by the position of the switchwhich has already been opened. We thus obtain a simplecircuit-arrangement which is beneficial to the reliability of service.

According to the invention, as means of extinguishing the tube thereenters into account more particularly a circuit-arrangement wherein thetube has connected in parallel with it the seriesconnection of anextinguishing condenser, an

auxiliary condenser and a switch, preferably an auxiliary dischargetube, whilst the ratio between the capacities is so chosen that thereturning switching Voltage is substantially taken up by the auxiliarycondenser. This will be explained more in detail in the followingdescription of the drawing.

The invention will be explained more fully with reference to theaccompanying drawing which diagrammatically represents, by way ofexample, one embodiment thereof.

Referring to Fig. 1 a source of direct-current voltage I is connectedthrough the intermediary of a mechanical switch 2 to a load 3. Inparallel with the switch 2 is connected a gasor vapourdischarge tube Awhich comprises a mercury cathode. 5 and a controlling member 6 in theform of an immersed ignition electrode of high resistance or acapacitative ignition electrode. Finally, in parallel with the tube lare connected furthermore in the known manner a switch i and a condenser8 which, for example, has been charged beforehand by a source ofcharging potential It with the polarity indicated.

Upon assuming that the load 3 is supplied via the switch 2 which isclosed at first, the diagram shown functions as follows:

The switch 2 is opened with the result that between the contacts thebeginning of an arc is struck. Then the tube 3 is ignited with the aidof the ignition electrode 5 so that the are at the switch 2 is takenover by the tube. This is accomplished by means of a charged condenserl5, the charge being obtained from a source of charging potential 22.Subsequently the tube is extinguished by closing the switch I, owing towhich the anode voltage of the tube is suiiiciently reduced by thecharged condenser 8 and, if required, the anode even acquires for ashort time a sufiiciently negative potential to extinguish the tube.

According to the invention, the tube is ignited within a limited periodof time 161 so that sparking or arcing to a degree detrimental to thecontacts does not occur. In the figure, the largest length of the arebetween the contacts which is allowable in this connection is denoted bya. The maximum time 151 is determined therefore by the quotient betweenthe distance a and the rapidity of opening of the contacts, whichrapidity should have, as the case may be, a certain minimum value onaccount of the requirements to be satisfied but, on the other hand, istied down from the point of view of construction to a certain maximum.The ignition of the tube 4 within the period in set therefore may occur,for example, dependently upon the position of the movable switch arm 2by means of an additional contact switch 24 or in the case ofelectromagnetic switching off with the aid of a properly chosen time inany known manner as will be explained more fully with reference to Fig.2. According to the invention, use is made furthermore of a tube 4 of sosmall dimensions and after being ignited, this tube is extinguishedafter a period, t2 of so short duration that re-ignition of the tube bythe returning switching voltage I is prevented. I

The behaviour of the switching tube may be explained with reference toFig. 3 which shows qualitatively the course of Paschens breakdown curvefor a rarefied gas, and wherein the breakdown voltage VD has beenplotted as a function of the product pd of gas pressure and electrodespacing. Detailed information relative Paschens curve may be found inApplied Electronics, a publication of The Technology Press,Massachusetts Institute of Technology. During the switching operationthe tube is in a state which is characterized by that portion of thecurve which is located to the left of the minimum. At the end of theperiod 151 the tube is in a state indicated by a point A. When the arcburns during the period of time 152 the pressure increases so that atthe end of this period at a point B the valve (pd z is reached. Thispoint corresponds to the voltage VB. Re-ignition does not occur as longas care is taken to ensure that VB exceeds the returning voltage V.

As may be seen from the figure, at a given voltage V this condition mayalways be fulfilled if the product pd on the branch AB remains below adetermined critical value (pd)2. In the above mention is made of thesteps with the aid of which this may be efiected in accordance with theinvention.

The tube is extinguished by closing the switch 1, which may also beeffected dependently upon the switch 2 or, as the case may be,dependently upon the ignition impulse at the electrode 6.

Finally, the periods t1 and 152 must be so chosen that, in connectionwith the opening rapidity of the switch 2 and with the additionalde-ionization means which, as the case may be, may be employed, withinthe total of the period t1+t2 the space between the contacts denoted inFig. 1 by b is, as has been set out in detail hereinbefore, in a stateso as to prevent the renewed production of an are between the contactsafter the tube has been extinguished. In the case illustrated thedistance b-a constitutes therefore a measure for the time period t2, ifonly the opening rapidity of the switch is taken into account.

Although Fig. 1 refers to the switching off of direct-current voltage,which has hitherto still been considered in practice as most diflicultlyrealizable alternating voltage may also be switched off in a forcedmanner in accordance with the invention at any point within the cycle,for example within one tenth of a half-cycle.

Fig. 2 represents a device according to the invention wherein the switch2 of Fig. 1 consists of two mechanical switches 9 and I located inseries and coupled with one another. The switch I0 comprises anadditional auxiliary switch I i, owing to which the correct moment ofignition of the tube 4 is fixed by means of a battery l2, a relay !3,contacts l4 and a charged condenser l5, condenser I5 being charged by asource of charging potential 22. The construction of the contacts [4 andI6 is such that a short and, as the case may be, regulable moment (t2)after the closure of the first-mentioned contacts the last-mentionedcontacts are closed, owing to which the tube 17 is ignited with the aidof a charged condenser l8, charged by a source 23, with the result thatthe condenser 8 charged by the device I9 (see also Fig. 1) is dischargedvia an auxiliary condenser through the tube 4, the tube beingextinguished by this impulse. Relatively to the condenser 8 theauxiliary condenser 20 is so dimensioned that it substantially takes upthe switching voltage which returns after the tube 4 has beenextinguished. This is particularly advantageous in switching highvoltages because the comparatively large extinguishing condenser neednot be insulated with respect to the returning high voltage since thedischarge in the tube l1 breaks off timely after the condenser 20 hasbeen charged. In the case of a periodically operating device it isadvisable to shunt the condenser 20 by a leakage resistance 2|, owing towhich a 6 sufiicient discharge of the condenser within the period oftime available therefore can be obtained.

It will be evident that known means other than the relay shown may alsobe utilized to ensure that the tube is ignited and extinguished at thecorrect moments.

With a circuit-arrangement utilized experimentally voltages of about 20kilovolts and, on the other hand, currents up to 200 amperes wereswitched with the aid of a mechanical switch and a gas discharge tubewherein the distance between the electrodes amounted to a fewcentimetres and which had a volume of approximately cube cms.

What I claim is:

1. Apparatus for disconnecting a load from a power source, saidapparatus comprising a mechanically operated switch interposed betweensaid load and said source and having a pair of contacts separable afteropening at a prescribed rate, a gaseous discharge device having acathode connected to one of said contacts, an anode connected to theother contact and an ignition electrode, a first normally open switchingelement, a first charged capacitor for providing a firing pulse andconnected between said electrode and said cathode through said firstelement, means responsive to the operation of said switch to close saidfirst element subsequent to the moment at which said switch is openedthereby igniting said device for a first predetermined period, a secondnormally open switching element. a second charged capacitor forproviding an extinguishing pulse and connected between said cathode andsaid anode through said second element, and means responsive to theoperation of said switch to close said second element at the terminationof said first period thereby to extinguish said device for a secondpredetermined period immediately succeeding said first period, saidcontacts during said first period being so spaced whereby an arcthereacross is not detrimental to said contacts, said contacts duringsaid second period having a sufficiently wide spacing and the spacebetween the contacts being sufficiently de-ionized to prevent arcingbetween the contacts, said device having a Paschens curve characteristicwherein the product of electrode spacing and gas pressure existing atthe end of said second period has a value effecting a magnitude ofbreakdown voltage for said device greater than is supplied by said powersource whereby re-ignition of said device subsequent to said secondperiod is prevented.

2. Apparatus for disconnecting a load from a power source, saidapparatus comprising a mechanically operated switch interposed betweensaid load and said source and having a pair of contacts separable at apredetermined rate after opening, a gaseous discharge device having acathode connected to one of said contacts, an anode connected to theother of said contacts and an ignition electrode, a first normally openswitching element, a first charged capacitor for providing a firingpulse and connected between said cathode and said electrode through saidfirst element, a second normally open switching lement, a second chargedcapacitor for providing an extinguishing pulse and. connected betweensaid anode and said cathode through said second element, anelectromagnetic relay for actuating said first and second elements,means responsive to the operation of said switch for actuating saidrelay, said relay being arranged to close said first element subsequentto the moment at which said switch is opened thereby igniting saiddevice for a first predetermined period, said relay being furtherarranged to close said second switch at the termination of said firstperiod thereby extinguishing said device for a second predeterminedperiod immediately succeeding said first period, said contacts duringsaid first period being so spaced whereby an are thereacross is notdetrimental to said contacts, said contacts during said second periodhaving a spacing sufficiently wide and the space between the contactsbeing sufliciently de-ionized to prevent arcing between the contacts,said device having a Paschens curve characteristic wherein the productof electrode spacing and gas pressure existing at the end of said secondperiod has a value effecting a magnitude of breakdown voltage greaterthan is supplied by said power source, whereby re-ignition of saiddevice subsequent to said second period is obviated.

3. Apparatus for disconnecting a load from a power source, saidapparatus comprising a mechanically operated switch interposed betweensaid load and said source and having a pair of contacts separable at apredetermined rate after opening, first and second gaseous dischargedevices each having a cathode, an anode and an ignition electrode, thecathode and anode of said first device being connected to said pair ofcontacts, first and second normally open switching elements, first andsecond charged capacitors for producing firing pulses, said firstcapacitor being connected between the cathode and ignition electrode ofsaid first device through said first element, said second capacitorbeing connected between the cathode and ignition electrode of saidsecond device through said second element, a third charged capacitor forproviding an extinguishing pulse and connected between the cathodes ofsaid first and second devices, means intercoupling the anodes of saidfirst and second devices, an electromagnetic relay for actuating saidfirst and second elements, means responsive to the operation of saidswitch for actuating said relay, said relay being arranged to close saidfirst element subsequent to the moment at which said switch is openedthereby igniting said first device for a first predetermined period,said relay being further arranged to close said second switch at thetermination of said first period thereby igniting said second device andextinguishing said first device for a second predetermined periodimmediately succeeding said first period, said contacts during saidfirst period being so spaced whereby an arc thereacross is notdetrimental to said contacts, said contacts during said second periodhaving a spacing sufiiciently wide and the space between the contactsbeing sufficiently deionized to prevent arcing between the contacts,said first device having a Paschens curve characteristic wherein theproduct of electrode spacing and gas pressure existing at the end ofsaid second period has a value efiecting a magnitude of breakdownvoltage greater than is supplied by said power source wherebyre-ignition of said first device subsequent to said second period isobviated.

4. Apparatus as set forth in claim 3, wherein said means forintercoupling the anodes of said first and second devices comprises acondenser connected in parallel with a resistor.

ADRIANUS CORNELIS V,AN DORSTEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 490,178 Thomson Jan. 17, 1893500,629 Thomson July 4, 1893 1,681,196 Rudenberg et a1. Aug. 21, 19281,691,395 Langmuir Nov. 13, 1928 1,691,423 Alexanderson et al. Nov. 13,1928 1,750,581 Egg Mar. 11, 1930 1,902,958 Jackson Mar. 28, 19331,975,164 Ludwig Oct. 2, 1934 2,071,447 Young Feb. 23, 1937 2,157,925Stoddard May 9, 1939 2,215,804 West Sept. 24, 1940 2,221,569 Berkey Nov.12, 1940 2,223,523 Ludwig Dec. 3, 1940 2,537,383 Van Dorsten Jan. 9,1951 FOREIGN PATENTS Number Country Date 129,999 Switzerland Dec. 22,1927 419,274 Great Britain Nov. 8, 1934 894,223 France Dec. 8, 1944

